1. Field of the Invention
The present invention relates to a method for controlling a back light in a portable radio communication terminal, and in particular, to a method for controlling the back light by using a clock function in a portable radio communication terminal.
2. Description of the Related Art
A portable radio communication terminal generally has a back light function to offer convenience to the user, when used in a dark condition. Referring to FIG. 1, a portable radio communication terminal having the back light function includes a display 10, a keypad 20, and a back light composed of a plurality of light emitting diodes (LEDs) 30.
FIG. 2 illustrates a known schematic block diagram of a back light control device. With reference to the drawing, a controller 100 controls the overall operation of the portable radio communication terminal. The controller 100 is a one-chip microprocessor having a ROM (read only memory) into which a control program is stored, and a RAM (random access memory) into which data generated in the course of executing the control program is temporarily stored. A timer 600 for performing a clock function displays current time on the display 10 under the control of the controller 100. A keypad 200 is composed of a number of numeric keys and function keys to generate key data when any one of a plurality of keys is depressed by the user. The key data generated is provided to the controller 100. A counter 300 begins counting the time under the control of the controller 100, and provides the controller 100 with a control signal after a lapse of a predetermined time. A power controller 400, connected to the controller 100, provides a back light 800 with a supply voltage under the control of the controller 100. The back light 800 is composed of a plurality of LEDs.
FIG. 3 illustrates a flow chart for controlling the back light control device shown in FIG. 2 according to the prior art. Now, referring to FIGS. 2 and 3, if the user operates the keypad 200, controller 100 checks at step 510 whether key data is received from the keypad 200. If the key data is received, the power controller 400 provides the back light 800 with the supply voltage under the control of the controller 100 at step 520, so as to turn on the back light 800. Thereafter, controller 100 enables counter 300 at step 530. The counter 300 provides the controller 100 with a counting completion signal after a lapse of a predetermined time. If the counter 300 generates the counting completion signal at step 540, the power controller 400 will cut off the supply voltage being supplied to the back light 800, under the control of the controller 100, at step 550, so as to turn off the back light 800. However, if the counter 300 has not generated the counting completion signal at step 540, the procedure will return to step 520 to repeat the foregoing steps 520 to 540.
Further, the portable radio communication terminal uses a battery to supply the power. Thus, it is very important to reduce a power consumption of the portable radio communication terminal so as to extend an operating time of the battery.
TABLE 1 ______________________________________ Current Consumption Operating Mode (Vcc = 5 V) Remarks ______________________________________ Stand-by 10-50 mA Rx Status Max. Output Tx. 300-500 mA Tx and Rx Status Back light 200-250 mA 10 LEDs Used ______________________________________
Table 1 expresses current consumptions of the portable radio communication terminal according to various operating modes, in which one LED consumes about 20 mA in a back light mode. It can be noted from Table 1 that the power consumption in the back light mode is much higher than that in the stand-by mode. Generally, the portable radio communication terminal is commonly used in a bright condition rather than in a dark condition.
However, upon receiving any key data, the conventional back light control device turns on the back light unconditionally, thereby wasting the power unnecessarily in the daytime. Thus, the operating time of the battery may be undesirably reduced. In particular, when the portable radio communication terminal is installed in a hands-free kit, the back light is always turned on even if the user does not operate the keypad, which causes unnecessary power consumption and a heat radiation during the daytime.